Conventionally, in a process for manufacturing a semiconductor device, a series of processes is performed upon the surface of a substrate such as a semiconductor wafer (referred to as a `wafer` hereinafter). That is, a circuit pattern is contracted and exposed upon a photo-resist formed on the substrate's surface using a photo-lithography technique, and then the substrate is developed.
During these coating and developing processes, a wafer is coated with a resist, exposed, and then developed. The wafer is heated (baked) before and after these processes, if necessary. Namely, there are performed so-called dehydration baking for drying the wafer, so-called pre-baking (PREBAKE) for heating and removing the resist solution included in the resist, so-called post-exposure baking (hereinafter referred to as `PEB`) performed between exposure and development, post-baking (POBEBAKE) performed after development, and so forth.
A heat processing apparatus performing such heat processing comprises a base disposed in a process container for mounting a wafer and a heat generator (such as a heater) buried inside the base. The heat generator heats to a high temperature (such as 120.degree. C.) to heat the wafer. With the influence of this heat generator, the temperature around the base will also rise to approximately 120.degree. C.